<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title> CSS Scroll Snap 2 Test: scroll-start interaction with scroll-snap</title>
  <link rel="help" href="https://drafts.csswg.org/css-scroll-snap-2/#scroll-start">
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
</head>


<body>
  <style>
    body {
      margin: 0px;
    }

    .spacer {
      height: 200px;
      width: 100px;
    }

    .scroller {
      height: 220px;
      width: 100px;
      overflow: scroll;
      scroll-snap-type: both mandatory;
    }

    #single_snap_scroller {
      scroll-start: 100%;
    }
    #multi_snap_scroller {
      scroll-start: 350px;
    }

    .snap_point {
      width: 100px;
      height: 200px;
      scroll-snap-align: start;
    }
  </style>
  <div id="single_snap_scroller" class="scroller">
    <div id="top_spacer" class="spacer"></div>
    <div id="lone_snap_point" class="snap_point"></div>
    <div id="bottom_spacer" class="spacer"></div>
  </div>
  <div id="multi_snap_scroller" class="scroller">
    <div id="snap_point_1" class="snap_point"></div>
    <div id="snap_point_2" class="snap_point"></div>
    <div id="snap_point_3" class="snap_point"></div>
  </div>
  <script>
    test((t) => {
      assert_equals(single_snap_scroller.scrollTop,
        top_spacer.getBoundingClientRect().height,
        "scroller snaps to top of snap point");
    }, "snap overrides scroll-start position");

    test((t) => {
      // scroll-start sets the initial scroll offset to 350px which is closer to
      // the third snap point than the second, so the scroller should snap to
      // the third snap_point.
      assert_equals(multi_snap_scroller.scrollTop,
        multi_snap_scroller.scrollHeight - multi_snap_scroller.clientHeight,
        "scroller snaps to snap point closer to start position.");
    }, "scroller snaps based on scroll-start position");
  </script>
</body>
